Magnetic recording media are widely used in various applications, particularly in the computer industry. A portion of a conventional recording medium 1 utilized in disk form in computer-related applications is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically of metal, e.g., an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (“DLC”), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium 1, the magnetic layer 13 can be locally magnetized by a write transducer or write head, to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer 13, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
It is considered desirable during reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head as close to the associated recording surface as is possible, i.e., to minimize the “flying height” of the head. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
Meanwhile, the continuing trend toward manufacture of very high areal density magnetic recording media at reduced cost provides impetus for the development of lower cost materials, e.g., polymers, glasses, ceramics, and glass-ceramics composites as replacements for the conventional Al alloy-based substrates for magnetic disk media. However, poor mechanical and tribological performance, track mis-registration (“TMR”), and poor flyability have been particularly problematic in the case of polymer-based substrates fabricated as to essentially copy or mimic conventional hard disk design features and criteria. On the other hand, glass, ceramic, or glass-ceramic materials are attractive candidates for use as substrates for very high areal density disk recording media because of the requirements for high performance of the anisotropic thin film media and high modulus of the substrate. However, the extreme difficulties encountered with grinding and lapping of glass, ceramic, and glass-ceramic composite materials have limited their use to only higher cost applications, such as mobile disk drives for “notebook”-type computers.
As employed herein, the term “glass” is taken to include, in the broadest sense, non-crystalline silicates, aluminosilicates, borosilicates, boroaluminosilicates, as well as polycrystalline silicates, aluminosilicates, and oxide materials; the term “ceramic” is taken to include materials consisting of crystalline particles bonded together either with a glass (i.e., vitreous) matrix or via fusion of the particles at their grain boundaries, as by sintering, as well as refractory nitrides, carbides, and borides when prepared in the form of bodies, as by sintering with or without a glass matrix or a silicon- or boron-containing matrix material, e.g., silicon nitride (Si3N4), silicon carbide (SiC), and boron carbide (B4C); and the term “glass-ceramics” is taken to include those materials which are melted and fabricated as true glasses, and then converted to a partly crystalline state, such materials being mechanically stronger, tougher, and harder than the parent glass, as well as non-porous and finer-grained than conventional polycrystalline materials.
Presently, media anisotropy for obtaining high performance magnetic recording media is typically achieved by circumferentially polishing (“mechanically texturing”) Al alloy substrates with NiP plating layers thereon by using a diamond or other relatively hard abrasive in slurry form dispensed on an absorbent and compliant polishing pad or tape. The circumferential texture pattern, produced by holding the surface of a rotating disk substrate against the polishing pad or tape with the abrasive slurry therebetween, simultaneously fulfills two desirable purposes: (1) tribologically—by minimizing stiction and friction at the head-disk interface; and (2) enhancing magnetic anisotropy—by providing a preferred orientation of the subsequently deposited polycrystalline Cr underlayer 12 and Co-based magnetic layer 13 along the circumferential textture lines of the pattern, resulting in an in-plane circumferential vs. radial anisotropy which improves the read/write parameters (e.g., coercivity Hc, residual magnetic susceptibility Br, coercive squareness S*, magnetic anisotropy Kμ) of the Co-based magnetic alloy layer.
The aforementioned circumferential texturing is thus effective for improving wear resistance and read/write characteristics of thin-film magnetic recording media; however, the benefits of texturing vary greatly upon the microscopic contours of the texture surface. Specifically, in order to form a medium having uniform magnetic characteristics, the microscopic contours of the texture surface must be made uniform.
Sub-micron flyability (e.g., <0.5 μ inch) of the recording transducer or head over a patterned media surface and enhanced media anisotropy thus are basic and essential requirements for obtainment of very high areal density recording media. However, attempts to achieve the requisite surface topography (e.g., substantially uniform texture patterns of desired contour or depth) on glass, ceramic, or glass-ceramic composite substrates utilizing conventional slurry-based abrasive polishing techniques have been unsuccessful due to their extreme hardness (e.g., glass substrates have a Knoop hardness greater than about 760 kg/mm2 compared with 550 kg/mm2 for Al alloy substrates with NiP plating layers). In addition, the low flowability and extreme hardness of these substrate materials effectively preclude formation of texture patterns in the surfaces thereof by injection molding or stamping, as is possible with polymer-based substrates.
In view of the foregoing, there exists a need for improved methodology for providing substrates for magnetic recording media, e.g., disk-shaped substrates, constituted of very hard, high modulus materials, with at least one surface thereof having requisite topography for enabling operation with flying head read/write transducers/heads operating at very low flying heights and with a texture provided therein for enhancing media anisotropy, e.g., by mechanical texturing. More specifically, there exists a need for an improved methodology for texturing, i.e., unidirectional mechanical texturing, of a surface of a substrate for a magnetic recording medium, comprised of a glass, ceramic, or glass-ceramic composite material, for reducing head-disk stiction/friction and for enhancing media anisotropy. In addition, there exists a need for an improved, high areal density magnetic recording medium including a high hardness, high modulus substrate having a textured surface for enhanced media anisotropy, e.g., a mechanically textured surface.
The present invention addresses and solves problems and difficulties attendant upon the use of very hard, high modulus materials, e.g., glasses, ceramics, and glass-ceramics, as substrate materials in the manufacture of very high areal density magnetic recording media, while maintaining fill capability with substantially all aspects of conventional automated manufacturing technology for the fabrication of thin-film magnetic media. Further, the methodology and means afforded by the present invention enjoy diverse utility in the manufacture of various other devices and media requiring formation of mechanically textured surfaces on high hardness materials.